In the drilling and production of oil and gas wells, a well bore is drilled by means of a plurality of drill pipes provided in sufficient numbers to assemble a rotatable drill string sufficient to drill the required depth. The rotatable drill string is terminated by a drill bit and typically provided with stand-off stabiliser parts periodically throughout the length of the drill string. The drill string is rotated to remove formation ahead of the drill bit, to drill out and thus form a wellbore, and to increase the depth of the well. Drilling mud or other fluid is circulated through the drill string to cool, lubricate and clear the drill bit of cuttings, and to displace the resulting drill cuttings from the bottom of the well to the surface, via an annulus formed between the drill string and the wall of the wellbore.
Periodically, the drill bit is removed from the wellbore and a casing comprising lengths of tubular casing sections coupled together end-to-end is run into the drilled wellbore and cemented in place. A smaller dimension drill bit is then inserted through the cased wellbore, to drill through the formation below the cased portion, to thereby extend the depth of the well. A smaller diameter casing is then installed in the extended portion of the wellbore and also cemented in place. If required, a liner comprising similar tubular sections coupled together end-to-end may be installed in the well, coupled to and extending from the final casing section. Once the desired full depth has been achieved, the drill string is removed from the well and then a work string is run-in to clean the well. Once the well has been cleaned out, the walls of the tubular members forming the casing/liner are free of debris so that when screens, packers, gravel pack assemblies, liner hangers or other completion equipment is inserted into the well, an efficient seal can be achieved between these devices and the casing/liner wall.
The step of cleaning the wellbore is usually achieved by inserting a work string containing dedicated well clean-up or cleaning tools or subs. Typical well cleaning tools known for use in this environment include scrapers, wipers and/or brushes which are held against the internal wall of the casing/liner, to clean away debris as the tool is run-in and then pulled out of the wellbore.
After a number of cleaning operations have been conducted, the cleaning elements, e.g. scrapers or bristles, can become worn, contaminated, clogged with debris and detritus, or otherwise deteriorated from design functionality. Therefore, when the work string is pulled out of hole, the cleaning sub tool requires servicing and the cleaning elements replaced or remediated. This normally entails break out of the tool sub from the string, and dismantling of the tool. This activity requires technically skilled labour to ensure that the tool is correctly assembled e.g. correct torque settings are applied; involves risk of error or potential damage to the tool e.g. fastener thread stripping; and also takes the tool out of action for the inevitable downtime associated with shipping back to the workshop for the aforesaid redressing operations.
It is amongst the objects of at least one embodiment of the present invention to obviate or mitigate at least one of the foregoing disadvantages.